Soot Particle Activation in Contrail Formation Using LES

Aircraft contrails form when water vapor in engine exhaust freezes on engine-emitted particles, potentially producing persistent ice clouds that contribute to climate warming. Understanding soot particle activation is therefore important for developing mitigation strategies. In this study, large eddy simulations (LES) were coupled with an online microphysical model that includes soot hygroscopicity through the κ-parameter, allowing a more realistic description of water uptake and activation. Simulations were performed for a LEAP-1A engine under representative cruise conditions to examine the effects of three parameters: soot hygroscopicity, initial soot number emissions, and initial soot core radius. Hygroscopicity values of κ = 0.0005, 0.005, and 0.0142 were considered, corresponding to equivalent fuel sulfur contents of 50, 410, and 1270 ppm. Additional cases varied the soot emission index from 1013 to 1015/kg-fuel and the soot core radius from 10 to 30 nm. The results show that lowering κ from 0.0142 to 0.0005 slightly decreases mean ice particle radius but increases the activated fraction by about 20%, due to greater water vapor availability. Reducing soot number emissions from 1015 to 1013 #/kg-fuel increases the mean ice particle radius from about 0.3 to 2.4 µm within 1 s and raises the activated fraction by about 66%. Increasing the initial soot core radius also enhances activation by about 20%, with its strongest effect occurring during the early stages of contrail development.